Bump coverage from 5.1 to 5.2 in /src/requirements (#577)

Bumps [coverage](https://github.com/nedbat/coveragepy) from 5.1 to 5.2.
- [Release notes](https://github.com/nedbat/coveragepy/releases)
- [Changelog](https://github.com/nedbat/coveragepy/blob/master/CHANGES.rst)
- [Commits](https://github.com/nedbat/coveragepy/compare/coverage-5.1...coverage-5.2)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Co-authored-by: dependabot-preview[bot] <27856297+dependabot-preview[bot]@users.noreply.github.com>

src/requirements/dev.txt

@@ -2,7 +2,7 @@
 
 django-debug-toolbar==2.2
 factory_boy==2.12.0
-coverage==5.1
+coverage==5.2
 codecov==2.1.7
 black==19.10b0
 pre-commit==2.6.0